The disclosed invention is about a pneumatic radial tire. More particularly, the present invention is directed towards a tire comprising a belt package wherein the belt ply edge separation is reduced by selective segmenting of the belt plies.
Conventional pneumatic belted radial tires include at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread. The belt plies are arranged so that the left and right cords are inclined at angles of 15xc2x0 to 30 with respect to the equatorial plane of the tire.
During operation of the tire, the belt ply edge separation can occur. The problem is generally attributed to the interlaminar shear strain or the strain energy density at the edge of the belt plies. Edge effect is best explained by the simple fact that the belt is very stiff while the adjacent rubber has a much lower stiffness. A smoother transition from the belt to the adjacent rubber will reduce the amount of interlaminar shear strain and the strain energy density.
To reduce the strain at the edges of the belt, it has been conventional practice to gradually reduce the belt ply widths. In such a tire design, the greatest width belt ply is adjacent the tire carcass layers and the narrowest width belt ply is closet to the overlying tread. Other known means of attempting to reduce the belt edge separation include employing overlay plies at the belt edges, cushion rubbers at the belt edges, or varying the modulus of the coating rubber in the differing belt layers.
Exemplary patents of other attempts to reduce belt edge separation include U.S. Pat. Nos. 4,140,166, 3,791,218, 3,757,843, and 5593523.
The present invention is directed towards a pneumatic radial tire. The tire is comprised of a reinforcing belt structure wherein the belt plies are divided into at least three segments. The reinforcing cords in each segment of a ply are oriented in the same inclination direction. By maintaining the same cord inclination in the segments, dividing the belt ply into segments creates hinge points for the belt ply, reducing the stiffness of the ply across the width of the tread from the centerline of the tire to the tread edges.
In one aspect of the present invention, if the belt structure has more than one reinforcing ply, the segments of the adjacent plies are staggered by a distance at greater than the radial height between the radially inner side of the adjacent belt plies.
In another aspect of the invention, the adjacent segments of each ply are separated by a distance u that is not greater than the radial thickness of the ply if the belt structure is a single ply, or a distance u that is not greater than the radial height h between the radially inner surface of the adjacent belt plies if the belt structure is comprised of more than one ply.
In another aspect of the invention, the central segments of the divided belt plies have an axial width of 20 to 80 percent of the tread width.
In another aspect of the invention, the divided plies of the belt structure has a central segment 34a, 36a, and two edge segments 34b, 36b, and the reinforcing cords of the central segment have a greater modulus value than the cords of the edge segments 34b, 36b.